1. Field of the Invention
The present invention relates to an engine with a centrifugal clutch. More specifically, the present invention relates to an engine which has a centrifugal clutch at an end of a crankshaft and an oil supplying configuration which supplies cooling and lubricating oil to the centrifugal clutch.
2. Description of the Related Art
A centrifugal clutch provided on a crankshaft of an engine typically has an inner member fixed to the crankshaft and a clutch housing fixed to a driven rotational member. The inner member has a centrifugal weight moved radially outward by a centrifugal force generated by rotation of the crankshaft. The centrifugal weight has a clutch shoe made of a friction member. The clutch housing has a cylindrical portion which is located radially outside and opposite the centrifugal weight and with which the clutch shoe of the centrifugal weight can be brought into contact. Such a centrifugal clutch generates heat due to friction heat between the clutch shoe and the cylindrical portion of the clutch housing. A cooling configuration is therefore necessary.
Japanese Patent Application Publication No. 2006-105132 discloses a centrifugal clutch of an engine having a cooling configuration. Oil is reserved in a lower portion of a clutch housing which houses the centrifugal clutch. A lower end of the clutch housing of the centrifugal clutch is immersed in the oil to cool the clutch housing.
In the above configuration according to the prior art, however, when the clutch housing is excessively immersed in the oil in order to improve a cooling effect, rotational resistance due to the oil is increased and a power loss of the crankshaft can be increased.
Aside the above cooling configuration, there is a cooling configuration which uses an oil passage formed in a crankshaft to supply oil to a centrifugal clutch. When the oil passage for cooling the centrifugal clutch is formed in the crankshaft, a journal portion of the crankshaft having the centrifugal clutch is supported by a bearing such as a ball bearing or a roller bearing. The oil thus cannot be supplied from the oil passage of a crankcase to the oil passage in the crankshaft via the bearing. In the prior art, an oil chamber is formed or a bearing metal having an oil hole is arranged adjacent to the bearing, so that the oil is supplied from the oil passage in the crankcase to the oil passage formed in the crankshaft and then to the centrifugal clutch.
In the configuration which has the oil chamber or the like formed adjacent to the bearing such as the ball bearing or the roller bearing, a length of the crankshaft becomes longer and a width of an engine in a direction of the crankshaft becomes larger. Particularly in an engine which couples a drive pulley of a V-belt type continuously variable transmission to a centrifugal clutch provided at the end of a crankshaft, the length of the engine in the direction of the crankshaft becomes longer.